Dark trace display device employing uv phosphor plus photochromic resin inside the display screen which generates color by means of triplet-to-triplet absorption

ABSTRACT

An information display screen viewable in high ambient light and darkness using a photochromic material capable of forming a dark trace and a luminescent trace. The photochromic material is molecularly dispensed in a rigid, transparent matrix. The photochromic materials used are polynuclear aromatic hydrocarbons and nitrogen containing heterocyclic compounds.

[ 3,744,77 JuIy 10, I973 DARK TRACE DISPLAY DEVICE EMPLOYING UV PHOSPHOR PLUS PHOTOCHROMIC RESIN INSIDE THE DISPLAY SCREEN WHICH GENERATES COLOR BY MEANS OF TRIPLET-TO-TRIPLET ABSORPTION Inventor: Robert Franz Stamm, Stamford,

Conn.

Assignee: Kiifefi''ah' flnliiif'fifi,

Stamford, Conn.

Filed: June 24, 1971 Appl. No.: 156,268

US. Cl. 350/160 P, 252/301.2, 260/590, 313/92, 343/17 Int. Cl. G021 l/36 Field of Search 350/160 P, 83.3 UV; 313/92 R References Cited UNITED STATES PATENTS 1/1972 Stamm et al. 350/160 P Ill 3,329,648 7/1967 Chopoorian 350/160 P 3,453,604 7/1969 Geusic et al.... 350/160 P 3,548,236 12/1970 Kiss 313/92 R 3,238,841 3/1966 Bjelland et a1. 350/160 P 3,214,383 10/1965 Moore et a1 350/160 P Primary Examiner-Ronald L. Wibert Assistant Examiner-V. P. McGraw Attorney-Charles Joseph F ickey [57] ABSTRACT An information display screen viewable in high ambient light and darkness using a photochromic material capable of forming a dark trace and a luminescent trace. The photochromic material is molecularly dispensed in a rigid, transparent matrix. The photochromic materials used are polynuclear aromatic hydrocarbons and nitrogen containing heterocyclic compounds.

6 Claims, 21 Drawing Figures PMENFED JUL 1 M975 3, 744.877

sum 01 or 1 INVENTOR.

ROEEET kAA/z 5m ATTORNEY PAIEMH, JUL 1 0:913

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R05 5/27 RANZ. STA/14M ATTORNEY DARK TRACE DISPLAY DEVIQE EMPLOYING UV PHOSII-IOR PLUS PIIOTOCIIROMIC RESIN INSIDE THE DISPLAY SQREEN WHICI-I GENERATES COLOR BY MEANS OF TRIPLET-TO-TRIPLET ABSORPTION This invention relates to a method and means for displaying real time information. It more specifically relates to a method and means for displaying information as dark traces with photochromic compounds activatable by ultraviolet radiation. It further relates to cathode ray tube display tubes or display panels making use of triplet--triplet photochromic compounds, where the image is self erasable. Numerous types of dark trace display devices are known. Some of these are cathode ray devices known as dark trace cathode ray tubes, for example such as shown in US. Pat. No. 2,409,606. Such tubes make use of materials which develop color centers under electromagnetic radiation or electron beam bombardment. The color centers thus form a visible image viewable by transmitted or reflected light. Typical suitable materials for forming color centers were alkali halides. These tubes were dark trace storage tubes, i.e. the image once formed remained until erased or if it faded spontaneously it was over a period of hours. The method of erasing was usually by a heat filament in the tube, causing considerable difficulty with heat dissipation before a reuse of the tube. It will be further realized that the uses of such a tube could not include display of real time information, i.e. information continuously changing with time.

Other types of information displays in panel form are shown in U.S. Pat. No. 3,238,841 making use of photochromic materials such as spiropyrans in a plastic film. Such displays involve moleculartransformations in the spiropyrans and are thus inherently slow. Moreover, these images are also storage images and have to be erased.

Cathode ray tube display devices are also well known which utilize phosphorescent screens, e.g. television or oscilloscope tubes, to display information as a glowing image in real time. These devices suffer from the disadvantage that their visibility is not good if the ambient light striking the viewing surface is very bright.

I have now discovered a display device which is a totally new concept. This device displays information as a dark trace, which is self bleaching, fading slowly with time. Moreover, the trace also has luminescent emission so that it is also visible in the dark. Thus it is possible to display real time information in high or low ambient light or in total darkness. The device makes use of photochromic compounds which are of the triplettriplet type disclosed in Canadian Pat. No. 781,707, which are polynuclear aromatic compounds, deuterated or undeuterated including nitrogen containing heterocyclics. The photochromic activity of such compounds has been known, but not very useful due to their high activity making it necessary to use them at low temperature. However, as disclosed in the Canadian Patent, these compounds, when dispersed molecularly in a suitable rigid organic or inorganic matrix are stabilized and useful at room temperature. It has now been found that such compounds in a matrix are activatable by ultraviolet radiation. Thus by the use of a phosphor activatable by a cathode ray and emitting in the ultraviolet range, a cathode ray tube display device having the characteristics described is constructed. A variation of this device can also be made where the cathode ray tube contains only the phosphor and the photochromic material is incorporated in an external screen. In addition, a photochromic screen can be used with an ultraviolet laser and means to provide an X Y scan and intensity variation of the ultraviolet beam to produce a dark trace image on the screen.

The dark trace images formed are visible in high ambient light as well as in the dark, and fade in from about one, to 20 or more seconds. Thus these display devices are useful for displaying real time information slowly changing with time. A particularly good application is for radar display where the required persistence of the image is of the order of a few seconds.

It is therefore an object of this invention to provide a display device, viewable in high ambient light and in darkness and which is self erasable.

A further object of the invention is to provide a dark trace display device capable of displaying real time information.

Another object is to provide a dark trace cathode ray tube capable of real time information.

A further object is to provide new triplet-triplet photochromic compounds of high efficiency for use in information display.

These and other objects of the invention will become apparent from consideration of the following description taken in conjunction with the appended claims and the drawings wherein:

FIG. 1 is a cross-sectional view of one embodiment of a display cathode ray tube according to the invention with dark trace screen and activating screen inside the tube;

FIG. 2 is a systematic representation of a projection display system using a cathode ray tube as in FIG. 1;

FIG. 3 is a systematic representation of a projection display system where the dark trace display screen is external to and separated from an activating cathode ray tube;

FIGS. 3A and 3B are focusing systems which may be used in the system shown in FIG. 3;

FIG. 4 is a systematic representation of a projection display using a separate dark trace screen as in FIG. 3, activated by an ultra-violet laser beam system;

FIGS. 5 and 6 are diagramatic representations of radar systems using the display device of the invention. edge film FIGS. 7 to 19 demonstrate performance characteristics of the triplet-triplet photochromic display devices of the invention.

Referring to FIG. 1 the information display device comprises an evacuated tube 10 provided with a screen 12 and with means in the form of an electron gun 14 for developing a ray of electrons l6 and directing the ray at the screen 12.

The screen 12 incorporates the photochromic T'--T compounds in a matrix as a layer 12A, a layer of a U.V. emitting phosphor 12B, and an aluminum layer 12C on the side struck by the cathode ray. In addition, a dichroic layer 12D may be coated on the T'-T layer facing the UV radiation to filter out UV and reflect visible light, especially for projection systems, as shown in FIG. 2.

The ray 16 of electrons is deflected horizontally by coils 20 and vertically by coils 22 to cause it to scan the screen 12. The ray 16 is focused on the screen 12 by an anode 26 in the form of a metallic coating on the inside surface of the tube 10.

In operation, ray 16 will be made to trace over screen 12 activating the U.V. layer which emits U.V. radiation and colors the screen at the places traced to form an image. The image will begin to fade from the screen when the electron bombardment ceases, and will persist for less than one to more than 20 seconds, depending on the specific T'T photochromic compound in the screen. The image may be viewed directly at the transparent end 28 of the tube.

In this embodiment the matrix for the PC compounds should be one that will not foul the vacuum, i.e. it does not break down and release gases. Such materials are for example Lexan polycarbonate (General Electric Co.) and glass resin Type 908 (Owens-Illinois Co.).

The photochromic materials are organic molecules 'molecularly dispersed in a colorless, rigid, organic polymeric or inorganic glass matrix. The thickness if from about 0.5 mm to 1.0 mm. By absorption of U.V. photons, a small percentage of the colorless molecules are converted to transient molecules which absorb in the visible spectrum. After cessation of excitation, the transients decay spontaneously and essentially unimolecularly to the colorless initial state. The time required to form the color depends on the incident flux, and with a pulsed laser emitting U.V., the color can be generated in times as short as 10 nsec. The time required for fading depends on the mean lifetime of the colored species. In a non-rigid medium (i.e., in liquid solutions), the mean lifetimes (e are generally in the milli-second region while in rigid media at room temperature, they approach values as great as 20 seconds.

Because of this spontaneous decay, the color does not require bleaching by light or heat, and white light projection systems can be employed. Contrast ratios achieved by diffuse relection are high enough to be of use in a practical sense. At 10 mW/cm (excitation by HgA3650A), they range from 5:1 to :1 for different materials; and at mW/cm values as high as 20:1 are obtained. To the human eye, a C.R. of 6:1 is definitely better than 3:1 but 12:1 does not represent a really marked improvement over 6:1. At these levels of excitation, to the eye, the sample appears to have the bulk of the color generated in less than 1 second; to an instrument, somewhat more time is required.

When employing excitation by a U.V. emitting phosphor, there is generally a long wave-length tail of violet to blue emission from the phosphor as well as emission of blue fluorescence from the PC. sample. This lowers the contrast ratio. However, if a broad-band yellow green filter is interposed, this unwanted emission is largely eliminated, and the contrast ratio is improved. This improvement is much more marked to an instrument than it is to the eye. The numerical values of CR. shown in FIGS. 7 to 17 were measured with a broad band yellow-green filter in front of the detector; the transmission curve of the filter is shown in FIG. 18.

A variety of colors can be achieved with the P.C. materials as shown in Table 1 TABLE I Max. Absorption Color to the Eye Blue Yellow BG,G,Y. Nearly Red (Magenta with very little blue) YG Magenta V,G, Y-Or Lilac (leaks Blue and Red) V,R Green (leaks Blue and Green) Most of Visible Blue-Gray 2 or 3 Green-Gray components Gray In order to achieve a iarge contrast to the human eye, the colored molecules should have maximum absorption at 555 nm. However, many persons acquire a strong distaste for this color when requried to view it for extensive periods of time. Thus, for such applications, two or three individual compounds may be mixed in order to obtain some type of gray which is generally considered more acceptable than magenta.

The T'T Photochromic Molecules Suitable compounds may be those which are recited in the following classes.

CLASS i All polynuclear aromatic hydrocarbons containing three ring or more whose hydrogen atoms contain the normal abundance (0.015%) of hydrogen of mass 2(deuterium=D), and the same hydrocarbons which have been deuterated and whose hydrogen atoms consist of about 40 percent or more of deuterium atoms.

Class II All members of Class I which are fused or condensed polynuclear aromatic hydrocarbons containing three or more rings whose hydrogen atoms contain the normal abundance (0.015%) of hydrogen of mass 2 (deuterium=D), and the same hydrocarbons which have been deuterated and whose hydrogen atoms consist of about 40 percent or more of deuterium atoms.

CLASS III Members of class I and II whose so-called or-bands are weak (for explanation of oz-bands see Polycyclic Hydrocarbons, Eric Clar, London, Academic Press, 1964, Vol. I, page 56 ff.), and whose hydrogen atoms contain the normal abundance (0.015%) of hydrogen of mass 2 (deuterium=D), and the same hydrocarbons which have been deuterated and whose hydrogen'atoms consist of about 40 percent or more of deuterium atoms.

CLASS IV Linear polyphenyls containing three to five rings whose hydrogen atoms contain the normal abundance (0.015%) of hydrogen of mass 2 (deuterium=D), and the same hydrocarbons which have been deuterated and whose hydrogen atoms consist of about 40 percent of deuterium atoms, which are connected in the 1-,2-, or 3-position of one terminal ring to benzophenone,

(or to some other suitable single or double energytransfer agent shown in Table II below), by one or more intervening -CH groups or by an oxygen (-O-) bridge.

CLASS V Certain highly-benzenoid or totally benzenoid molecules (see Clar. Vol. 1, p. 34) joined together in pairs, or linked to phenyl or xenyl groups in a manner such that they are capable of assuming para-quinoidal-like structures in the triplet state and are characterized by possessing an energy greater than about 18,000 cm when in the lowest triplet state whose hydrogen atoms contain the normal abundance (0.015%) of hydrogen of mass 2 (deuterium=D), and the same hydrocarbons which have been deuterated and whose hydrogen 5 atoms consist of about 40 percent or more of deuterium atoms.

Such compounds of class V include QR 0 x3 A W O 15 Q O where R can be: 20 O 25 I and where the possible points of phenyl or xenyl substitution are indicated by the black dots.

TABLE I1 Energy Transfer Agents Listed in Order of Magnitude b b of Lowest Excited E181) E(' I ic k sec Singlet Energy cm om Level (1) Triphenyl amine C H15N b 2L ,5o0 0.88 3.7

Acetophenone CSHBO TABLE II Conta Energy Transfer Agents Listed in Order of Magnitude of Lowest Excited Level (S1) E(1) Singlet Energy cm 1 2-Acetonaphthone Benzophenone C H O h-P henylbenzophenone 2-Naphthaldehyde l-Naphthyl phenyl Ketone zl zoo mums II Cont.

lunergy Transfer Agents Listed in Order of Magnitude of Lowest Excited Singlet Energy Level (S1) 9 (CH3)2N 0Q. V 7' PW? b,,.LL'-bis(dimethyI- amino)benzophenone' O 9,10-Anthraquinone Benzil CHI-H1002 Fluorenone S E 0 0 l,L;-maphthoquinone 10 16 9.

10 sec TABLE II. Cont.

Energy Transfer Agents Listed in Orderof Magnitude b of Lowest Excited E(S E('l t) 1c k sec Singlet Energy cm om Level Lil l] I 1 20,200 18,9oo ll l,l L-Benzoquinone C H O HO 4/ O c I (I) -18,ooo

1,2napthoquinone 1O 2 -15,ooo

1,2-3enzoquinone 2. finnolaevJjgllim. llllgys. 291829359862) HT )d a indicates a non-radiative reaction or transfer of ammon em. ys. etermln rom S, T, energy gap in this reference and from E(T in reference ((1) 55 energy]' The grourid staflte of the energy'transfer agent below. (ETA), the doner, IS excited by UV to its lowest excited sidman' Chem 956); 4'567 (957% singlet state and from there undergoes fast intersystem d. Turro, "Molecular Photochemistry," New York, W.A. Benjamin,

[M (196 crossing to its lowest triplet with high efficiency (100 =h Quantum yield for intersystem crossing into the triplet mani- 60 percent in some cases) It e transfers its plet e fo ergy downhill" to the lowest triplet state of the accepk Velocity constant or frequency factor for intersystem crossing. tor which is the" able to manifest absorption or The use of single or double energy transfer agents for T 8,, emission (phosphorescence). It is necessary fg g g f g g gtz gs isrsgf mm the that the initial absorption of UV should occur through p y e e p o 65 the donor (D) and that (T,) be higher than (T,)

SINGLE ENERGY TRANSFER DOUBLE ENERGY TRANSFER (DET) hv h v .,)D* mr wnu an (s.*

( 1*);- (T1)D a),1( i)A+ 0) Here the initial absorption of energy occurs in the acceptor or photochromic end of the molecule which then passes its excited singlet energy downhill" to the donor which then undergoes intersvstem crossing with high efficiency to its lowest triplet state after which it transfers its triplet energy downhill to the acceptor which can manifest T'T absorption or T S 06 5 5 e 319 ca? 5 2 @5 2 e emission (phosphorescence). Here it is necessary that (8 be higher than (8 and that (T be higher than (T,) In comparing the two types of energy transfer, it is true to say that SET generally occurs with greater efficiency but that overall, a greater concentration of triplet molecules of species A can be achieved from a given flux of UV photons by DET because the initial act of excitation can often occur with greater efficiency.

TABLE III Phenanthrene Chrysene Triphenylene Pyrene 3,h -Benzophenanthrene 1,2-Benzanthracene 1,2-Benzochrysene 1,2-Benzopyrene l,P-BJp-Dibenzanthracene Picene l,2-7,8-Dibenzochrysene l,2-6,7-Dibenzopyrene 11,12-13,llt-Dibenzopicene TABLE III Ccnt.

1,2,-3,Lt-5,6-7,G-Tetrabenzanthracene Dinaphthm-(E ,3'-1,2-); (2" ,3"-6,7-)pyrene Hexaphenyltriphenylene l1.-(Lt-methylamino-p-terphenyl)benzophenone.

-p-qu terphenyl -p-quinquepheny1) achievable with a steady-state light source. The last examples in Table serve to illustrate DET.

The primary absorption act occurs in the aminopoly- -phenyl moiety. This is followed by singlet-to-singlet transfer to benzophenone which undergoes intersystem crossing to the triplet state and then transfers its triplet energy back to the lowest triplet of the aminopolyphenyl which then manifests T'T absorption or T S emission. When R is p-terphenyl, the triplet color is yellow and the T T absorption is in the blue; for R as p-quatraphenyl, the color is pink and the T-T absorption is in the yellow-green region; whenlR is p-quinquephenyl the color is green with the T'T absorption being in the. red.

Table IV shows preferred T--T photochromic vcompounds.

TABLE IV Compounds of Preference for Dark-Trace CRT Compound Degree of (sec) 'Deu'teration P10. Color l.,2-5,,6-'D.iben-- 90% or better 70.5 Pink anthra'cene Picene 90% or better 10 Gray-Green 3.,l4-Benzotetraphene 90% or better 6.5 Purple 1 2-6 7-.Dibenzopyrene 9.0% or better 20 Pink l,2-3,h-5,'6-Tribenzanthra-cene 90% or better 19 .Pink

1.,2-Benzocoronene 90% or better 21 Blue-gray l,l2-2,3-10 ,ll- Tribenzoper'yl ene 0 7.5 Tan l,2-5.,6-Diben'zocoronene 90% or better 21 Green -3, ,-5, benzocoronene 90% or better 6.5 Golden Tan '3a'4" 97" n 3' 'I'etrabenzopentacene 90% or better 21 Green s '3! |-'5| 9 Tetrabenzanthracene 0 10.8 Pink 

2. The display screen of claim 1 wherein said means is an ultra-violet emitting phosphor.
 3. The display screen of claim 1 wherein said means is a laser emitting in the ultra-violet range.
 4. The display screen of claim 1 wherein said photochromic compound is self erasable.
 5. A display system as in claim 3 including means to provide an X-Y scan of said laser beam, and means to modulate the intensity of said beam.
 6. The display screen of claim 1 wherein said photochromic compound is deuterated. 